A variety of congenital, acquired, or induced syndromes are associated with insufficient numbers of erythrocytes (red blood cells or RBCs). The clinical consequence of such syndromes, collectively known as the anemias, is a decreased oxygen-carrying potential of the blood, resulting in fatigue, weakness, and failure to thrive. Erythropoietin (EPO), a glycoprotein of molecular mass 34,000 daltons, is synthesized and released into the systemic circulation in response to reduced oxygen tension in the blood. EPO, primarily synthesized in the kidney and, to a lesser extent, in the liver, acts on erythroid precursor cells (Colony Forming Units-Erythroid (CFU-E) and Burst-Forming Units-Erythroid (BFU-E)) to promote differentiation into reticulocytes and, ultimately, mature erythrocytes.
The kidney is the major site of EPO production and, thus, renal failure or nephrectomy can lead to decreased EPO synthesis, reduced RBC numbers, and, ultimately, severe anemia, as observed in predialysis and dialysis patients. Subnormal RBC counts may also result from the toxic effects of chemotherapeutic agents or azidothymidine (AZT) (used in the treatment of cancers and AIDS, respectively) on erythroid precursor cells. In addition, a variety of acquired and congenital syndromes, such as aplastic anemia, myeloproliferative syndrome, malignant lymphomas, multiple myeloma, neonatal prematurity, sickle-cell anemia, porphyria cutanea tarda, and Gaucher""s disease, include anemia as one clinical manifestation of the syndrome.
Purified human EPO or recombinant human EPO may be administered to patients in order to alleviate anemia by increasing erythrocyte production. Typically, the protein is administered by regular intravenous injections. The administration of EPO by injection is an imperfect treatment. Normal individuals maintain a relatively constant level of EPO, which is in the range of 6-30 mU/ml, depending on the assay used. After typical treatment regimens, serum EPO levels may reach 3,000-5,000 mU/ml following a single injection, with levels falling over time as the protein is cleared from the blood.
If a relatively constant level of EPO is to be provided in the blood (i.e., to mimic the normal physiology of the protein), a delivery system that is capable of releasing a continuous, precisely dosed quantity of EPO into the blood is necessary.
The present invention relates to transfected primary and secondary somatic cells of vertebrate origin, particularly mammalian origin, transfected with exogenous genetic material (DNA or RNA) that encodes a clinically useful product, such as erythropoietin (EPO) or insulinotropin (e.g., derivatives of glucagon-like peptide 1 (GLP-1), such as GLP(7-37), GLP(7-36), GLP-1(7-35), and GLP-1(7-34), as well as their carboxyl-terminal amidated derivatives produced by in vivo amidating enzymes and derivatives that have amino acid alterations or other alterations that result in substantially the same biological activity or stability in the blood as that of a truncated GLP-1 or enhanced biological activity or stability), methods by which primary and secondary cells are transfected to include exogenous genetic material encoding EPO or insulinotropin, methods of producing clonal cell strains or heterogenous cell strains that express exogenous genetic material encoding EPO or insulinotropin, methods of providing EPO or insulinotropin in physiologically useful quantities to an individual in need thereof, through the use of transfected cells of the present invention or by direct injection of DNA encoding EPO into an individual; and methods of producing antibodies against the encoded product using the transfected primary or secondary cells. Transfected cells containing EPO-encoding exogenous genetic material express EPO, and, thus, are useful for preventing or treating conditions in which EPO production and/or utilization are inadequate or compromised, such as in any condition or disease in which there is anemia. Similarly, transfected cells containing insulinotropin encoding exogenous genetic material express insulinotropin and, thus, are useful for treating individuals in whom insulin secretion, sensitivity, or function is compromised (e.g., individuals with insulin-dependent or non-insulin dependent diabetes).
The present invention includes primary and secondary somatic cells, such as fibroblasts, keratinocytes, epithelial cells, endothelial cells, glial cells, neural cells, formed elements of the blood, muscle cells, other somatic cells that can be cultured, and somatic cell precursors that have been transfected with exogenous DNA encoding EPO or exogenous DNA encoding insulinotropin. The exogenous DNA is stably integrated into the cell genome or is expressed in the cells episomally. The exogenous DNA encoding EPO is introduced into cells operatively linked with additional DNA sequences sufficient for expression of EPO in transfected cells. The exogenous DNA encoding EPO is preferably DNA encoding human EPO but, in some instances, can be DNA encoding mammalian EPO of non-human origin. EPO produced by the cells is secreted from the cells and, thus, made available for preventing or treating a condition or disease (e.g., anemia) in which EPO production and/or utilization is less than normal or inadequate for maintaining a suitable level of RBCs. Cells produced by the present methods can be introduced into an animal, such as a human, in need of EPO, and EPO produced in the cells is secreted into the systemic circulation. As a result, EPO is made available for prevention or treatment of a condition in which EPO production and/or utilization is less than normal or inadequate to maintain a suitable level of RBCs in the individual. Similarly, exogenous DNA encoding insulinotropin is introduced into cells operatively linked with additional DNA sequences sufficient for expression of insulinotropin in transfected cells. The encoded insulinotropin is made available to prevent or treat a condition in which insulin production or function is compromised or glucagon release from the pancreas is to be inhibited.
Primary and secondary cells transfected by the subject methods can be seen to fall into three types or categories: 1) cells that do not, as obtained, produce and/or secrete the encoded protein (e.g., EPO or insulinotropin); 2) cells that produce and/or secrete the encoded protein (e.g., EPO or insulinotropin), but in lower quantities than normal (in quantities less than the physiologically normal lower level) or in defective form, and 3) cells that make the encoded protein (e.g., EPO or insulinotropin) at physiologically normal levels, but are to be augmented or enhanced in their production and/or secretion of the encoded protein.
Exogenous DNA encoding EPO is introduced into primary or secondary cells by a variety of techniques. For example, a construct that includes exogenous DNA encoding EPO and additional DNA sequences necessary for expression of EPO in recipient cells is introduced into primary or secondary cells by electroporation, microinjection, or other means (e.g., calcium phosphate precipitation, modified calcium phosphate precipitation, polybrene precipitation, microprojectile bombardment, liposome fusion, or receptor-mediated DNA delivery). Alternatively, a vector, such as a retroviral vector, which includes exogenous DNA encoding EPO can be used, and cells can be genetically modified as a result of infection with the vector. Similarly, exogenous DNA encoding insulinotropin is introduced into primary or secondary cells using one of a variety of methods.
In addition to exogenous DNA encoding EPO or insulinotropin, transfected primary and secondary cells may optionally contain DNA encoding a selectable marker that is expressed and confers upon recipient cells a selectable phenotype, such as antibiotic resistance, resistance to a cytotoxic agent, nutritional prototrophy, or expression of a surface protein. Its presence makes it possible to identify and select cells containing the exogenous DNA. A variety of selectable marker genes can be used, such as neo, gpt, dhfr, ada, pac, hyg, mdr, or hisD genes.
Transfected cells of the present invention are useful as populations of transfected primary cells, transfected clonal cell strains, transfected heterogenous cell strains, and as cell mixtures in which at least one representative cell of one of the three preceding categories of transfected cells is present, as a delivery system for treating an individual with a condition or disease that responds to delivery of EPO (e.g., anemia), or for preventing the development of such a condition or disease. In the method of the present invention of providing EPO, transfected primary cells, clonal cell strains, or heterogenous cell strains are administered to an individual in need of EPO in sufficient quantity and by an appropriate route to deliver EPO to the systemic circulation at a physiologically relevant level. In a similar manner, transfected cells of the present invention providing insulinotropin are useful as populations of transfected primary cells, transfected clonal cell strains, transfected heterogenous cell strains, and as cell mixtures, as a delivery system for treating an individual in whom insulin production, secretion, or function is compromised or for inhibiting (totally or partially) glucagon secretion from the pancreas. A physiologically relevant level is one that either approximates the level at which the product is normally produced in the body or results in improvement of an abnormal or undesirable condition.
Clonal cell strains of transfected secondary cells (referred to as transfected clonal cell strains) expressing exogenous DNA encoding EPO (and, optionally, including a selectable marker gene) are produced by the method of the present invention. The present method includes the steps of: 1) providing a population of primary cells, obtained from the individual to whom the transfected primary cells will be administered or from another source; 2) introducing into the primary cells or into secondary cells derived from primary cells a DNA construct that includes exogenous DNA encoding EPO and additional DNA sequences necessary for expression of EPO, thus producing transfected primary or secondary cells; 3) maintaining transfected primary or secondary cells under conditions appropriate for their propagation; 4) identifying a transfected primary or secondary cell; and 5) producing a colony from the transfected primary or secondary cell identified in (4) by maintaining it under appropriate culture conditions and for sufficient time for its propagation, thereby producing a cell strain derived from the (founder) cell identified in (4). In one embodiment of the method, exogenous DNA encoding EPO is introduced into genomic DNA by homologous recombination between DNA sequences present in the DNA construct used to transfect the recipient cells and the recipient cell""s genomic DNA. Clonal cell strains of transfected secondary cells expressing exogenous DNA encoding insulinotropin (and, optionally, including a selectable marker gene) are also produced by the present method.
In one embodiment of the present method of producing a clonal population of transfected secondary cells, a cell suspension containing primary or secondary cells is combined with exogenous DNA encoding EPO and DNA encoding a selectable marker, such as the bacterial neo gene. The two DNA sequences are present on the same DNA construct or on two separate DNA constructs. The resulting combination is subjected to electroporation, generally at 250-300 volts with a capacitance of 960 xcexcFarads and an appropriate time constant (e.g., 14 to 20 msec) for cells to take up the DNA construct. In an alternative embodiment, microinjection is used to introduce the DNA construct containing EPO-encoding DNA into primary or secondary cells. In either embodiment, introduction of the exogenous DNA results in production of transfected primary or secondary cells. Using the same approach, electroporation or microinjection is used to produce a clonal population of transfected secondary cells containing exogenous DNA encoding insulinotropin alone, or insulinotropin and a selectable marker.
In the method of producing heterogenous cell strains of the present invention, the same steps are carried out as described for production of a clonal cell strain, except that a single transfected primary or secondary cell is not isolated and used as the founder cell. Instead, two or more transfected primary or secondary cells are cultured to produce a heterogenous cell strain.
The subject invention also relates to methods of producing antibodies specific for EPO. In these methods, transfected primary or secondary cells expressing EPO are introduced into an animal recipient (e.g., rabbit, mouse, pig, dog, cat, goat, guinea pig, sheep, or non-human primate). The animal recipient produces antibodies against the EPO expressed, which may be the entire EPO protein antigen or a peptide encoded by a fragment of the intact EPO gene. Polyclonal sera is obtained from the animals. It is also possible to produce monoclonal antibodies through the use of transfected primary or secondary cells. Splenocytes are removed from an animal recipient of transfected primary or secondary cells expressing EPO. The splenocytes are fused with myeloma cells, using known methods, such as that of Koprowski et al. (U.S. Pat. No. 4,172,124) or Kohler et al. (Nature 256:495-497, 1975) to produce hybridoma cells that produce the desired anti-EPO monoclonal antibody. The polyclonal antisera and monoclonal antibodies produced can be used for the same purposes (e.g., diagnostic, preventive, or therapeutic purposes) as antibodies produced by other methods. Similarly, antibodies specific for insulinotropin can be produced by the methods of the present invention.
The present invention is particularly advantageous in treating anemia and other conditions in which EPO production, utilization, or both is compromised in that it: 1) makes it possible for one gene therapy treatment, when necessary, to last a patient""s lifetime; 2) allows precise dosing (the patient""s cells continuously determine and deliver the optimal dose of EPO based on physiologic demands, and the stably transfected cell strains can be characterized extensively in vitro prior to implantation, leading to accurate predictions of long term function in vivo); 3) is simple to apply in treating patients; 4) eliminates issues concerning patient compliance (periodic administration of EPO is no longer necessary); and 5) reduces treatment costs (since the therapeutic protein is synthesized by the patient""s own cells, investment in costly protein production and purification facilities is unnecessary).